Hybridization, apomixis and polyploidy as evolutionary drivers of the maidenhair fern family (Pteridaceae) in the West Indies

• Applicants: Dr. Marc Appelhans; Dr. Ledis Regalado
• Subject Area: Evolution and Systematics of Plants and Fungi
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 540446503

Interspecific hybridization and polyploidization are widely recognized as major drivers of fern evolution. The combination of these processes can explain most of the phenotypic variation observed in extant species, particularly in closely related species complexes. Additionally, nearly 10% of ferns for which the reproductive mode has been determined exhibit apomixis, suggesting that this form of asexuality also plays an important role in fern evolution. Recent global analyses of polyploid biogeography have found high levels of polyploidy in several island systems, indicating a significant contribution of this evolutionary process to the diversification of established island lineages. The main goal of this project is to study the contribution of polyploidy, hybridization, and apomixis to the formation of endemic fern flora across an island system with a highly heterogeneous origin and geological complexity, such as the West Indies. This region is well known for its high number of local endemics, which represent approximately 40% of local fern flora. This fern flora has been hypothesized to be the result of a combination of immigration events from adjacent regions of tropical America and local speciation processes, especially in the Greater Antilles. However, the processes that lead to the formation of these endemic lineages remain unexplored. Our study model will be the family Pteridaceae, which is particularly well-suited to study such phenomena, especially some genera, such as Adiantum, Adiantopsis, Notholaena, and Pityrogramma. Previous studies on these groups have suggested the presence of hybrids, allopolyploid lineages, and presumable apomictic forms. We will then test to what extent hybridization, polyploidization and apomixis have contributed to speciation in those groups using for the first time on West Indian ferns a phylogenomic approach and a broad sampling covering the geographical range and morphological variation of the target groups. We will apply a combination of target enrichment (hybrid capture) and plastome sequencing. These data will be complemented by morphological, cytological, and reproduction mode data to complete an integrative assessment of these speciation events. Finally, increased sampling will also allow us to conduct new dating and biogeographic analyses, providing a historical context to test hypotheses about the origin, distribution, and continuity of polyploid and apomictic fern lineages in the West Indies.

• DFG Programme: Research Grants